1. Field of the Invention
The invention relates to devices for operating a track tension wheel on a tracked vehicle, and relates more specifically to a device of the type that comprises a tension wheel arm that has an axis of rotation at a first end, around which the arm can be pivoted in relation to the vehicle by means of a first drive member, which tension wheel arm carries the tension wheel at its other end, via a rocker arm that is mounted on the tension wheel arm in such a way that it can pivot around a spindle, and a second drive member for changing the distance between the central axis of the tension wheel and the center of rotation of the tension wheel arm by pivoting the rocker arm in relation to the tension wheel arm, in order thereby to adjust the tension of, or alternatively to replace, the vehicle's drive track that is running over the tension wheel, with the first drive member having a first end that engages with the tension wheel arm at a distance from the center of rotation of the tension wheel arm in such a way that it can pivot, and a second end that is connected to a first attachment in such a way that it can pivot, whereas the second drive member has a first end that is pivotally connected to a part that is connected to the rocker arm.
2. Description of the Related Art
In order to change and optimize the driving characteristics of a tracked vehicle to suit the surface upon which it is being driven, varying the vertical position of the tension wheel on the tracked vehicle between an upper position, in which the vehicle can be driven on a hard firm surface, and a lowered position, in which the vehicle can be driven on a soft yielding surface such as deep snow, soft ground or marshland, has previously been proposed. At the same time, it is desirable to keep the track tension somewhat lower when the tension wheel is raised, in order to have less wear on the track when driving on a hard surface, and to keep the track tension increased somewhat when the tension wheel is lowered, in order to reduce the specific ground pressure when driving on a soft surface.
A device of essentially the type described in the introduction that makes this possible is already known through FR 1 401 309 (see FIGS. 6 and 7). This device is not designed to be able to achieve an automatic tensioning of the drive track during the final phase of the lowering of the tension wheel arm. As a result of its design, the operating device for the tension wheel is bulky and can be easily damaged by external objects. In addition, on this device, the operating cylinder for pivoting the tension wheel arm upwards and downwards is permanently attached to the vehicle in such a way that it does not allow rapid springing movements of the tension wheel arm, when, for example, the tension wheel drives over a projecting object on the ground.
In SE 0301046-9 (SE 525 073 C), a device is also known for operating a track tension wheel on a tracked vehicle, which device has a tension wheel arm that can be adjusted telescopically in length, and achieves an automatic lengthening of the arm when this is lowered, in order at the same time to obtain a required tensioning of the associated drive track that runs around the tension wheel. The tension wheel arm is operated by two hydraulic cylinders that are mounted on the vehicle itself in such a way that they can pivot. As the hydraulic cylinders are mounted on the vehicle outside the actual tension wheel arm, the mechanical connections between the hydraulic cylinders and the arm and between the hydraulic cylinders and the eccentric mechanism can be exposed to external forces, in addition to which seals need to be arranged to protect the cylinders from the ingress of dirt. In addition, under certain circumstances, the automatic lengthening of the arm when it is pivoted down can create too strong a tension in the drive track in a horizontal position of the arm. In order to enable there to be springing movements of the arm when driving on uneven surfaces, one of the two cylinders can act as a shock absorber, by oil in the cylinder being allowed to flow through an associated regulator.